text: Proton reduction catalysts based on earth-abundant elements carry out one side of the water-splitting half-reaction.
  A mole of octahedral nickel(II) complex, [Ni(bztpen)] (bztpen = N-benzyl-N,N’,N’-tris(pyridine-2-ylmethyl)ethylenediamine) produced 308,000 moles of hydrogen over 60 hours of electrolysis with an applied potential of -1.25 V vs. standard hydrogen electrode.
  Ru(II) with three 2,2'-bipyridine ligands is a common compound for photosensitization used for photocatalytic oxidative transformations like water splitting. However, the bipyridine degrades due to the strongly oxidative conditions which causes the concentration of Ru(bpy)32+ to diminish. Measurements of the degradation is difficult with UV-Vis spectroscopy but MALDI MS can be used instead.
  Cobalt-based photocatalysts have been reported, including tris(bipyridine) cobalt(II), compounds of cobalt ligated to certain cyclic polyamines, and some cobaloximes.
  In 2014 researchers announced an approach that connected a chromophore to part of a larger organic ring that surrounded a cobalt atom. The process is less efficient than a platinum catalyst although cobalt is less expensive, potentially reducing costs. The process uses one of two supramolecular assemblies based on Co(II)-templated coordination of  (bpy = 2,2′-bipyridyl) analogues as photosensitizers and electron donors to a cobaloxime macrocycle. The Co(II) centers of both assemblies are high spin, in contrast to most previously described cobaloximes. Transient absorption optical spectroscopies indicate that charge recombination occurs through multiple ligand states within the photosensitizer modules.